*{
    margin: 0;
    padding: 0;
}
html,body{
    height: 100%;
}
.big{
    display: flex;
    flex-direction: column;
    height: 100%;
}
header{
    text-align: center;
    height: 40px;
    line-height: 40px;
}
main{
    flex: 1;
    background: url(../imgs/bg.jpg) no-repeat;
    background-size: 1200px;
    background-position: center;
    position: relative;
}
main>span{
    color: white;
    font-size: 48px;
    position: absolute;
    bottom: 15%;
    left: 20%;
    animation: move 2.5s ease-in-out;
}
@keyframes move {
    0%{
        bottom: 30%;
        opacity: 0;
    }
    100%{
        bottom: 15%;
        opacity: 1;
    }
}
.big main .small{
    width:105px;
    height: 40px;
    background: white;
    color: black;
    border-radius: 20px;
    text-align: center;
    line-height: 40px;
    position: absolute;
    right: 20px;
    top: 20px;
}
a{
    color: black;
    text-decoration: none;
}